I am using the xindy'xindy' package to compile the index containing Vietnamese. It works fine except the order within words. The "standard" order is accepted as the following, which is different from the current xindy'xindy' default order:
I edited the vietnamese/utf8.pl.in (attached below) and tested with this version. However, there are some words that are ordered in an unexpected way. The expected order, for example, should be,
But it is not sorted in that order, i.e., the two last numbers, 5 & 6, are now placed at the positions of 3 & 4. The same happened with words: Lan Làn Lản Lãn Lán Lạn (note the tonal diacritics).